This work is directed at developing an improved x-ray imaging detector for high-energy radio therapy applications and exploring its use as a two- dimensional dosimeter in-quantitative treatment verification. A high- performance portal imaging system will be a key factor in reducing localization problems, thereby contributing to lower recurrence of tumors at the margins of the treatment field. In the work proposed here, we will assemble an imaging system, using high density clear scintillating glass as the sensor and a slow scan CCD for read out. Glass scintillators have densities approaching 4 g/cm3, a value significantly greater than granular phosphor screens. The slow scan CCD will provide signal-to-noise ratios greater than possible with video tubes. We will perform tests to determine spatial resolution, signal-to-noise ratio, and Detective Quantum Efficiency in comparison to that of the Siemens Beam View Plus system, a conventional system based on metal/phosphor and electron beam video tube technology. Both systems will be calibrated with respect to dose, accuracy, and precision. The Phase I program will include experimental x- ray tests with the Rando phantom which could be useful in determining dose to the patient estimated from the exit dose distribution measured with the high performance portal imaging system.